The present invention is concerned with an on board refueling vapor recovery system for motor vehicles which functions to prevent fuel vapor displaced from the head space of the vehicle fuel tank during a refueling operation from being discharged into the atmosphere.
It is known in the prior art to provide a motor vehicle with an on board fuel vapor recovery system operable to prevent the emission of fuel vapor into the atmosphere via the fuel tank vent which functions to equalize pressure in the tank head space as fuel is withdrawn by operation of the vehicle engine. These prior art systems employ a vapor canister in the fuel tank vent line which will entrap the relatively small amount of fuel vapor expelled from the tank between refueling operations when the fuel vapor pressure within the tank exceeds atmospheric pressure. This prior art "running vapor" canister is connected to the intake manifold of the vehicle engine via a purge system which applies manifold vacuum to the canister to withdraw fuel vapor from the canister at a controlled rate for combustion in the engine. These particular prior art systems are designed with flow capacities which are totally inadequate to cope with the massive surge of fuel vapor displaced from the fuel tank during a refueling operation, and as a result vapor displaced by the incoming fuel is discharged into the atmosphere from the open end of the fuel tank fill pipe. In some states, service station fuel pumps are equipped with a system to recover this discharged fuel vapor.
In commonly owned co-pending application of Ser. No. 101,069 filed Sept. 25, 1987, there is disclosed a refueling vapor recovery system mounted on the vehicle which takes the form of a vapor flow passage and vapor receiving canister connected between the fuel tank and purge system in parallel with the fuel tank vent "running vapor" recovery system referred to above. This "on board" refueling vapor recovery system requires the provision of several additional components to the vehicle and space within the vehicle available for mounting these components and routing various conduits between the components is restricted and varies widely in location between various makes and models of vehicles.
Desirably, the active components, such as valves, of such a refueling vapor recovery system should be mounted at some location where they are reasonably accessible and closely adjacent each other to minimize the number of connections and conduits required to connect the components into the system.
The present invention is especially directed to a fill neck assembly physically located at the inlet end of the fuel tank fill pipe which incorporates in a single package the various valves, including emergency pressure relief valves, required by an on board refueling vapor recovery system.